Carbon dioxide (CO2) is one of the important bridges from the phenomenon of the body emerging into the mind. We might already know that deep breathing, or slower breathing, and various other breathing techniques are useful for reducing anxiety and keeping composure. The breathing techniques work directly through the vagus and other nerves to activate the parasympathetic nervous system. However, the gas composition changes in the blood from those techniques also work simultaneously and significantly to alter the organism's global metabolic state.
From our normal resting breath rate and metabolisms, an increase in CO2 will counter-intuitively increase aerobic metabolism. This will increase tissue perfusion and feel like relaxation. Many people talk about the need to breathe more oxygen(O2) and others demonize CO2 as an environmental toxin. On the back of basic physiology, I will challenge or add nuance to those views. To understand this uncommon CO2 perspective, we need to know two subtle pieces of carbon dioxide physiology: the bohr effect and the capillary gate activation mechanism.
Bohr’s Effect:
The Bohr effect is a name for the phenomenon in which oxygen’s binding affinity to haemoglobin is inversely proportional to acidity and its local concentration of CO2. Said another way, oxygen leaves haemoglobin and red blood cells easiest in environments with high CO2 and high bicarbonate. Bicarbonate is CO2 dissolved in water. Haemoglobin has four spots for either an oxygen molecule or a carbon dioxide molecule. In the lung the oxygen concentration is high and so is the binding affinity of oxygen. We can assume after leaving the lung that most or all four spots are bound with oxygen. This phenomenon very elegantly facilitates the delivery of oxygen where it is most needed. Carbon dioxide and carbonate production will be the highest where metabolic activity is the highest and O2 will therefore be directed to that source of higher metabolism. As a basic refresher aerobic metabolism can be summarized as:
oxygen + sugar becomes carbon dioxide + water + energy.
We can think of the whole body as a three dimensional field where CO2 pours out of metabolic hotspots like brains, and O2 moves up the gradient to the places of most oxygen demand. The paragraph below gives an example of the effect’s role on muscles:
The Bohr effect enables the body to adapt to changing conditions and makes it possible to supply extra oxygen to tissues that need it the most. For example, when muscles are undergoing strenuous activity, they require large amounts of oxygen to conduct cellular respiration, which generates CO2 (and therefore HCO3− and H+) as byproducts. These waste products lower the pH of the blood, which increases oxygen delivery to the active muscles.
Capillary Gate Mechanism:
In conjunction with the Bohr effect, carbon dioxide also drives many fundamental changes through the capillary gate mechanism. The presence of carbon dioxide directly stimulates nitric oxide (NO) for the vascular endothelium. While carbon dioxide is the primary capillary gate regulator, nitric oxide drives the vasodilation. Nitric oxide also makes the blood less viscous by inhibiting thrombin, opposing clot formation and dissolving clotting factors. Parasympathetic activation, temperature, sunlight, red light, infrared light and oxytocin all increase nitric oxide with similar effects to increased CO2. The same mechanisms that increase vasodilation and metabolism reduce the chances of conditions like stroke and heart disease as well as a number of other conditions less obviously related such as cancer. This article on oxytocin goes through a more thorough list of the conditions one would expect to resolve with increased vasodilation and peripheral metabolism. Increased volume and ease of fluid flow allow for a much increased tissue perfusion of blood and delivery of oxygen and carbohydrate. This mechanism will have a positive feedback with metabolism as increased oxygen and glucose drive increased carbon dioxide and nitric oxide production.
Hyperventilation:
Hyperventilation is simply excess breathing and is associated with hypocapnia. Hypocapnia is low CO2. Hyperventilation is a critical part of anxiety and panic. When someone hyperventilates they end up pushing ever more oxygen into the haemoglobin molecules of their red blood cells and transferring CO2 out of the body. This creates an environment of respiratory alkalosis. Alkalosis is a decrease in acidity or an increase in pH of the blood. Thanks to the Bohr effect, as the haemoglobin molecules fill up, and carbonate leaves the surrounding blood, the oxygen increases its affinity for the haemoglobin. Incrementally, with the capillary gates closing, the oxygen will stop accessing and transferring into active cells. Blood will be full of oxygen while the cells will be cut off and starving for inputs. The brain and other tissues will experience hypoxia. Hypoxia will activate the sympathetic nervous system and further increase the breath rate while spiking stress hormones like adrenaline and cortisol. The feedforward cycle can spiral into distressing physiological experiences often called panic. This is also why bag breathing, or rebreathing, was a common tool for unwinding a panic attack.
Anxiety Redefined:
Anxiety can be thought of as a persistent or recurring lower level hyperventilation coinciding with alkalosis, hypometabolism and hypothyroid conditions. Without sufficient aerobic metabolism there will be insufficient CO2 and NO to maintain peripheral vasodilation and parasympathetic activation. Aerobic metabolism is critical for the feeling of relaxation. The insufficient CO2 feeds into the nervous systems as sympathetic dominance and the brain releases stress hormones for lipolysis. Those same hormones also make cells less insulin insensitive. Mild hyperventilation will tend to maintain itself as the chemoreceptors initiating the drive to breath adapt to existing low levels of bodily CO2 and bicarbonate.
Hypoventilation:
Hypoventilation is under breathing, and usually corresponds with an excess of carbon dioxide; hypercapnia. Hypercapnia will counter-intuitively allow for greater cellular oxygen delivery and respiration thanks to the Bohr effect and the capillary gate mechanism. Underbreathing to the extent that it resets the chemoreceptors for breathing will move a person’s physiology towards vasodilation and increased metabolism in peripheral tissues. Similar effects can be had by increasing the partial pressure of CO2, exercising, increasing glucose intake and anything and everything that increases oxidative metabolism.
Mind and Body Exercises:
I speculate that hypoventilation is a significant causal component in driving the subjective experiences of various exercises and practices built around the breath. Restrained breathing while contracting larger muscles quickly escalates internal carbon dioxide. From my experience, the twisting poses in yoga always challenged my ability to breathe, likely helping reset those breath-craving chemoreceptors. Both swimming in pools and floating in warm isolation tanks leave me with the persistent feeling of full body relaxation. That feeling of whole body relaxation relates perfectly to increases in peripheral metabolism and associated tissue perfusion. Even meditation, which does not often engage muscles, is very likely to be training the chemoreceptors and breathing patterns for hypoventilation. Perhaps meditation is doing so through mental phenomena and increases in cognitive metabolism.
Relationships and Therapy:
Relationships that reduce the expected need for calorie retention, i.e. friendships, feel good and increase both the parasympathetic tone and related hormones to enable further tissue perfusion and repair. Various therapies work by also changing the body's forecasted metabolic needs. Predicting metabolic needs after discovering a false negative belief in a modality such as CBT should feel like having more surplus energy for future pursuits. Similarly, learning how to identify and articulate restrained emotions or thoughts in a domain such as emotions focused therapy would reduce the day to day caloric burdens of active suppression.
Evolutionary Context:
Evolutionary mismatches drive our high prevalence of anxiety and panic. The hypocapnia and hyperventilation of anxiety follow from preset tendencies to overbreathe and a disengagement of bodily activity from sympathetic nervous system activation. Hearts race, stress hormones surge, breath accelerates but muscles do not fire. In evolutionary terms, sympathetic activation would preempt an expected fight or flight activity. Running, punching, or wrestling would all significantly engage the body's muscles. The increased breathing would be appropriate to feed the new demand driven by those muscular contractions.
Other significant factors push us into pervasive hypocapnia and anxiety. Reduced social connectivity, inadequate sun exposure, circadian arrhythmia, diets for hibernation, and diet and chewing that obstructs airways as well as environmental chemicals put the brakes on metabolism and respiration. Many people, if not most people, in the modern world are starting off with normals that are fairly anxious. Cognitive hypoxia from hyperventilation readily encourages deeper panic spirals. Engaging the body’s muscular oxygen demand, especially while holding one’s breath can be a simple way to return to baseline in the short run.
Exercise Caution:
Working out without adequate caloric replenishment; however, may make the anxiety even more of a future problem. In my experience, that pattern can result in a vicious cycle and something like addiction to exercise as the main source of relaxation. In the medium and long run, lifestyle choices that increase metabolism while engaging regular practices that desensitize the chemoreceptors, make everyday normal much less anxious. I intend to cover an ecology of approaches in later articles.
Primary Sources of Inspiration:
50 Years Lost In Medical Advance: The Discovery of Hans Selye's Stress Mechanism
Genes, Carbon Dioxide and Adaptation.
Breath: The New Science of a Lost Art
Jaws: The Story of a Hidden Epidemic
Quick or Direct Anxiety & Panic Resources:
When Panic Attacks: The New, Drug-Free Anxiety Therapy That Can Change Your Life
The website of David D. Burns, MD | 022: Scared Stiff — What Is Anxiety? (Part 1) (Podcast)
Anxiety, Panic Disorder, and Depression - Patrick McKeown (Video)
*The above resources/authors are fantastic and worth referencing and using, but they don’t see the full picture, nor do they need to for their approaches to work. Neither focus on the level of metabolism for the production of CO2. TCBT will reduce the metabolic costs of thoughts and Butyenko breathing will give practices to consciously engage the parasympathetic nervous system and retrain the chemoreceptors.
Articles Referenced:
Bohr Effect:
Autonomic Nervous System:
Capillary Gate:
30 Years Lost in Medical Theory: Part VII The Capillary Gate Mechanism (Video)
Carbon dioxide:
Bench-to-bedside review: carbon dioxide
Hypercapnia increases brain viscoelasticity
Hypercapnia: permissive and therapeutic
Effect of episodic hypoxia on sympathetic activity and blood pressure
Exposure to hypoxia produces long-lasting sympathetic activation in humans
Cerebral vasomotor reactivity during hypo- and hypercapnia across the adult lifespan
Red Lights
Stroke
Seasonality of stroke in Finland
Nitric Oxide:
Erythrocytes and Vascular Function: Oxygen and Nitric Oxide
Nitric oxide from neuronal NOS plays critical role in cerebral capillary flow response to hypoxia
Role of Nitric Oxide in the Cerebral Vasodilatory Responses to Vasopressin and Oxytocin
Cerebral blood flow regulation by nitric oxide: recent advances
Nitric oxide in immunity and inflammation
New issues about nitric oxide and its effects on the gastrointestinal tract
Chemoreceptors:
Human respiratory system - Chemoreceptors
*The above article is important and contrary to most of the fitness community advocating calories in calories out blah blah, or even high fat low carb diets. I used to be in that camp. Adrenaline is one of a few catecholamines required to liberate fat for emergency energy use. People feel ‘great’ not realizing they are in sympathetic dominance undermining tissues, especially brain and endocrine tissues requiring repair from parasympathetic activation.